Perhaps your girl is absent-minded, and that's why she keeps leaving her phone in your car and at your crib. Just be aware that she might have more duplicitous designs. Unlike many recording apps, Night Recorder will work in stand-by mode. The app is meant to record sounds that you make in your sleep like snoring and teeth-grinding. There may be other night sounds that aren't exactly made while sleeping, and this app is going to pick those up too. The sounds are outputted to small, convenient audio files perfect for saving until the end of divorce proceedings (or dramatic breakups).
Whatever you say (or moan) can and will be used against you in the court of your girl.